[bread_butter]

I’d imagine if Reddit were to do it we’d be up in our arms.

[boomboomsubban]

Reddit does have a list of blocked domains, apparently they even wholesale block things on the .ru top level domain.

[johnnyanmac]

Reddit the business, or Reddit the subreddit managed by free mods?

The former does do this, and has for a very long time. The mods of each subreddit can ban whatever domain they want.